Bypass Flow Passage Outlet Design for Air Flow Sensor Accuracy
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Solution Overview
Problem
Conventional thermal-type air flow measuring devices for internal combustion engines suffer from negative-side errors due to pulsation in intake air flow, especially with the popularization of exhaust gas recirculation, which increases the amplitude of pulsation and leads to backward flow, causing measurement inaccuracies and pressure drop issues.
Innovation Solution
The air flow measuring device incorporates a housing with a bypass flow passage that includes a vertical and non-vertical outlet opening on its outer wall, allowing the intake air to flow through a longer passage length, reducing backward flow and pulsation amplitudes, and adjusting the intersecting angle between the openings to control the inflow of backward flow, thereby minimizing negative-side errors without increasing pressure drop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the passage length L2 of the bypass flow passage is made longer than L1, then the negative-side error of the measurement value is reduced, but the pressure drop in the bypass flow passage deteriorates
Solution Approach 1:
The outlet of the bypass flow passage is divided into multiple openings (first opening and second opening) with different orientations. This segmentation allows the flow to be distributed through multiple paths, reducing the overall pressure drop while maintaining the beneficial thermal convection effect of the extended passage length for measurement accuracy.
Solution Approach 2:
Different openings are provided with different local characteristics (vertical and non-vertical orientations) to optimize flow distribution. The first opening is provided perpendicular to the flow direction while the second opening is provided non-perpendicularly, creating locally optimized flow patterns that reduce pressure drop while maintaining measurement precision.
2Adaptability or versatility
If the amplitude of intake air pulsation increases due to exhaust gas recirculation, then backward flow is generated, but the negative-side error increases
Solution Approach 1:
The outlet is segmented into multiple openings with different orientations to handle bidirectional flow. The first opening (perpendicular) and second opening (non-perpendicular) work together to detect both forward and backward flow components, allowing the sensor to accurately measure air flow rate despite pulsation-induced backward flow while minimizing negative-side error.
Solution Approach 2:
The two openings are provided with asymmetric orientations (one perpendicular, one non-perpendicular to the flow direction). This asymmetric configuration enables the system to differentiate between forward and backward flow components, improving measurement accuracy during pulsation conditions without requiring symmetric treatment of flow directions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces negative-side errors and improves measurement accuracy by limiting backward flow into the bypass passage, maintaining measurement precision without deteriorating pressure drop, thus enhancing the reliability of air flow rate measurements.
Implementation Method 1
a sensor that is accommodated in the bypass flow passage to produce the electrical signal as a result of heat transfer between the sensor and the taken-in intake air
Data Source
AI summary
An air flow measuring device takes in part of intake air flowing through an intake passage. The device includes a housing and a sensor. The housing defines a bypass flow passage through which taken-in intake air passes and which has an outlet that opens on an outer wall of the housing. The sensor is accommodated in the bypass passage to produce an electrical signal as a result of heat transfer between taken-in intake air and the sensor. The outlet of the bypass passage includes vertical and non-vertical openings. The vertical opening opens toward a downstream side of a flow of intake air in the intake passage and is provided perpendicular to the flow of intake air. The non-vertical opening is provided non-perpendicularly to the flow of intake air in the intake passage. The outlet is a continuous stretch of opening where the vertical and non-vertical openings are continuously formed.